In multiple access networks, the various stations normally consist of a transmitter and a receiver. They are usually located within a limited range of ten kilometers or less and any station may be connected to any other station. For a passive network, the distribution requirements are efficiently realized with a star coupler.
Workstations, which will normally include a transmitter and a receiver, can be located in various rooms of a building or various buildings on a campus. If each of the transmitters operates with a different optical carrier frequency, then the complete comb of signals will appear at each output port of the star. Thus, each receiver has access to each transmitter in the same manner that a radio receiver has access to the entire broadcast spectrum.
An N.times.N passive star coupler can be used to provide a high performance optical data network to interconnect many users at gigabit rates. Ignoring excess losses, a signal incident on any input port is divided equally among all the output ports. The average power at each of the N output ports of the star is equal to the incident power at each of the N input ports. But, the power per channel at each output port is equal to only 1/N of the incident power in that channel. This loss which is due to splitting cannot be efficiently recovered by an amplifier at either the input port or the output port of the star coupler unless the saturation power of the amplifier is increased to be substantially N times the value of the power transmitted. A simple and economical arrangement for demultiplexing the various channels is also needed.